Cat tree



FIG. 1 is a perspective view of a cat tree showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof; and,

FIG. 6 is a top plan view thereof.

The broken lines in the drawings illustrate portions of the cat tree that form no part of the claimed design. 

CLAIM The ornamental design for a cat tree, as shown. 